The invention relates to a device for isolating stacked blanks with at least one blank stop and at least one conveyor belt.
Isolating devices of this type are employed to supply blanks of paper to folded-bag gluing machines at a prescribed rhythm. This function is carried out in a device known from German OS 2 946 426 by means of conveyor belts that can be raised and lowered. A stack of blanks is placed on the belt guides upstream of a stop in the form of two positioning tongues located approximately the thickness of one blank above the belt. The belts are raised by means of one or more eccentric shafts, intercepting the undermost blank and conveying it though a gap between the stop and the belt, which is maintained in position from below, to the infeed of a folding-and-gluing machine. As the eccentric shaft continues to turn, the conveyor belts are continuously lowered into their disengaged position and then raised again until they intercept the next blank and remove it from the bottom of the stack.
Prerequisite to the smooth removal of the blanks, however, is the least possible slippage between the blank and the belt, which assumes in turn that as much of the surface of the blank as possible is in contact with as much of the surface of the belt as possible.
In order, accordingly, to ensure that the separate blanks are supplied to the folding-and-gluing machine at a prescribed rhythm and at intervals that, aside from changes in the program, are uniform, providing the conveyor belts with suction openings that communicate with a source of vacuum is also known. The suction temporarily positions the undermost blank more or less stationary on the belt.
Even this measure, however, does not always ensure non-slipping removal or isolation of the blanks, which are often concave or convex along or across the direction of travel. Since the curvature depends on the orientation of the fibers in the blank and on its drying behavior during the manufacturing process, it is irregular and cannot be counteracted by adjusting the conveyor belts and/or belt guides.